1. Field of the Invention
This invention concerns a fuel hose mainly used for automobiles. More particularly, this invention relates to a fuel hose showing excellent impermeability to alcohol-mixed gasoline where methanol, ethanol, or the like is mixed. The fuel hose of this invention can also be used suitably as a pipeline for an alcohol fuel cell or a hydrogen fuel cell, for example, in automobiles.
2. Description of the Related Art
In recent years, there has been a demand for decreasing atmospheric release of gasoline in view of environmental problems. Therefore, regulations against permeation of gasoline have become more and more severe for fuel hoses for use in automobiles. Conventional single layered hoses composed of NBR/PVC cannot satisfy such regulations sufficiently.
In view of the above, it has been considered to provide a thin film of a resin layer on the innermost layer of a fuel hose. Resin materials have higher impermeability to gasoline than rubber materials. Further, when the resin layer is formed of a thin film, the flexibility of the fuel hose can be maintained. Specifically, it has been proposed to provide a thin film polyamide resin layer or a thin film fluororesin layer on the innermost layer of a fuel hose.
For instance, Japanese Patent Application Laid-Open No. 118549/1996 discloses laminating a tubular body of unvulcanized rubber of epichlorohydrin and an extruded fluororesin layer and adhering them by vulcanization. Japanese Patent Application Laid-Open No. 255004/1994 discloses electrostatically coating a powdery fluororesin to the inner circumferential surface of a tubular body of vulcanized rubber and then forming a fluororesin layer by heating and cooling. In the fuel hoses described above, more excellent impermeability than that of a single layered rubber hose can be expected for ordinary gasoline.
Recently, in view of the toxicity of MTBE (methyl tert-butyl ether) added to gasoline as an octane number improver, attention has been paid to the change to an alcohol-mixed gasoline. However, the alcohol-mixed gasoline has a rather high gasoline permeability not only to rubber materials, but also to resin materials. The reason is probably that when alcohol having low molecular weight selectively permeates, gasoline induced by the alcohol also permeates, resulting in the high gasoline permeability.
According to studies by the inventors, when a polyamide resin layer or a fluororesin layer is formed on the innermost layer, it is not easy to reduce the film thickness of the resin so as to ensure required flexibility of a fuel hose while simultaneously ensuring the sufficient impermeability to the alcohol-mixed gasoline.
In view of the regulations against fuel permeation expected to be enforced from the year of 2004 in the United States, there has been a strong demand for a fuel hose capable of conforming to severe regulations for impermeability to gasoline including alcohol-mixed gasoline.